1. Field of the Invention
The present invention relates generally to a container crane driving control system, and more particularly, to a container crane driving control system using an AC motor system.
2. Description of the Related Art
A container crane loads or unloads containers into or from a container ship which is brought alongside a wharf.
Conventionally, an DC motor system is used to drive and control this type of container crane, since a great torque and accurate torque control are required to lift and lower a heavy container and to hoist a heavy boom.
Operation of this type of container crane has four modes: a main hoisting mode for lifting and lowering containers, a travel mode for causing a crane to travel, a boom hoisting mode for hoisting and lowering a boom and a trolley mode for causing a container to make a traverse motion.
The main hoisting mode and the travel mode cannot be performed simultaneously, and the boom hoisting mode and the trolley mode cannot be performed simultaneously. Hence, the container crane driving control system comprises a first driving control apparatus for controlling both the main hoisting mode and the travel mode and a second driving control apparatus for controlling both the boom hoisting mode and the trolley mode. In general, a leonard apparatus (thyristor leonard apparatus) is used as the main hoisting controller. The leonard apparatus controls an armature voltage of a DC motor, with a speed feedback, by means of a switching circuit using a switching element such as a thyristor, and controls a field current of the DC motor by means of another switching circuit. The others controller each are a voltage controller without a velocity feedback.
The aforementioned conventional container crane driving control system will be described with reference to FIG. 1.
An AC power source 10 is connected to a first driving control apparatus 20 and a second driving control apparatus 30.
The first driving control apparatus 20 comprises a main hoisting DC motor 21; eight traveling DC motors 22-1 to 22-8; an armature voltage thyristor circuit 23 for controlling both an armature voltage of the main hoisting DC motor 21 and armature voltages of the eight traveling DC motors 22-1 to 22-8; a field current thyristor circuit 24 for controlling the field current of the main hoisting DC motor 21; a field current thyristor circuit 25 for controlling the field currents of the traveling DC motors 22-1 to 22-8; a speed feedback circuit 26; five contactors 27-1 to 27-5 for individually connecting and disconnecting the main hoisting DC motor 21 and the traveling DC motors with the armature voltage thyristor circuit 23; four protecting circuits 28-1 to 28-4 for protecting the traveling DC motors 22-1 to 22-8; and four regulation resistor 29-1 to 29-4 connected to field circuits of the traveling DC motors 22-1 to 22-8.
An armature circuit of the main hoisting DC motor 21 is connected to the armature voltage thyristor circuit 23 and the contactor 27-1. A field circuit of the main hoisting DC motor 21 is connected to the field current thyristor circuit 24. The armature voltage thyristor circuit 23 A/D converts an output from the AC power source 10 and supplies a desired DC voltage to the armature circuit of the main hoisting DC motor 21. The field current thyristor circuit 25 A/D converts an output from the AC power source 10 and supplies a desired DC current to the field circuit of the main hoisting DC motor 21. The speed feedback circuit 26 is constituted by a tacho-generator (TG) 26B connected to the rotational shaft of the main hoisting DC motor 21 via a joint 26A. A speed signal, detected by the tacho-generator (TG) 26B, is supplied to the armature voltage thyristor circuit 23.
The armature circuits of the first and second traveling DC motors 22-1 and 22-2 are connected in series and the field circuits thereof are also connected in series. The armature circuits of the third and fourth traveling DC motors 22-3 and 22-4 are connected in series and the field circuits thereof are also connected in series. The armature circuits of the fifth and sixth traveling DC motors 22-5 and 22-6 are connected in series and the field circuits thereof are also connected in series. The armature circuits of the seventh and eighth traveling DC motors 22-7 and 22-8 are connected in series and the field circuits thereof are also connected in series. As a result, the eight traveling DC motors 22-1 to 22-8 are constructed as a four-series motor system. The four-pairs motor system performs a speed matching operation. The armature circuits of the series are connected to the armature voltage thyristor circuit 23 and are also connected to the contactors 27-2 to 27-5 and the protecting circuits 28-1 to 28-4, respectively. The field circuits of the series are connected to the field current thyristor circuit 25 and are also connected to the regulation resistor 29-1 to 29-4, respectively. The protecting circuits 28-1 to 28-4 respectively comprise current detectors 28A-1 to 28A-4, inserted in the armature circuits; and overload current relays 28B-1 to 28B-4. The armature voltage thyristor circuit 23 A/D converts an output from the AC power source 10 and supplies a desired DC voltage to the armature circuits of the traveling DC motors 22-1 to 22-8. The field current thyristor circuit 25 A/D converts an output from the AC power source 10 and supplies a desired DC current to the field circuits of the traveling DC motors 22-1 to 22-8.
The second driving control apparatus 30 is a leonard apparatus similar to the first driving control apparatus 20. However, the first driving control apparatus 20 has a circuit configuration for controlling one main hoisting apparatus and eight traveling DC motors, whereas the second driving control apparatus 30 has a circuit configuration for controlling one boom hoisting DC motor and one or two trolley DC motors.
In the conventional container crane driving control system as shown in FIG. 1, since the main hoisting mode and the travel mode cannot be performed simultaneously, the contactors 27-2 to 27-5 are open, when the contactor 27-1 is closed. In contrast, when the contactor 27-1 is open, the contactors 27-2 to 27-5 are closed. Thus, the armature circuit of the main hoisting DC motor 21 and the armature circuits of the traveling DC motors 22-1 to 22-8 can be selectively activated by the armature voltage thyristor circuit 23. As a result, the armature circuits of the main hoisting DC motor and the traveling DC motors 22-1 to 22-8 are simplified. In addition, the torque of the main hoisting DC motor can be large and can be can performed a speed matching operation with a high accuracy, thereby accurately lifting and lowering heavy containers. The same applies to the boom hoisting operation and trolley operation by the second driving control apparatus 30.
Since the above-described conventional container crane driving control system is a DC motor system, the a commutator of the DC motors must be maintained at intervals, and the brushes of the DC motor must be exchanged. Moreover, since the container crane is placed in a bay area such as a wharf, the DC motor system, which cannot easily be totally enclosed, has a structural drawback in that it is likely to suffer from salt damage.